Tavi Gevinson, the 16-year-old fashion and editorial wunderkind behind the über cool teen website Rookie, was on Late Night with Jimmy Fallon last night to promote her new book Rookie Yearbook One. As if she wasn't impressive enough, Gevinson managed to bowl Fallon and the entire audience over with her charm and humor. The whole interview's a blast, but the biggest highlight has to be Tavi's brief tutorial in cultivating the perfect bitchface. Jimmy takes to it like a fish to water.